| dc.description.abstract | This thesis uses an established high-pressure solid oxide fuel cell (SOFC) testing platform with interconnectors forming a single-cell stack to measure the cell performance and electrochemical impedance spectroscopy (EIS) of an ammonia SOFC with a planar anode-supported cell (Ni-YSZ/YSZ/LSC-GDC, 50 *50 mm2). Experiments are conducted in a high-temperature, high-pressure and fuel concentration of solid oxide fuel cell (SOFC). Both hydrogen and ammonia fuel are used under various temperature and pressure conditions, so that effects of temperature and pressurization on the cell performance and EIS of ammonia SOFC can be explored. Then we compare the results of both ammonia and hydrogen SOFC. Experimental conditions are as follows. We apply constant flow rates, i.e. anode fuel: (1) 540 sccm H2 + 360 sccm N2 or (2) 360 sccm NH3 +180 sccm N2; cathode air: 900sccm. Ammonia contains three hydrogen atoms, which is 1.5 times higher than hydrogen. Thus, the ammonia flow rate is adjusted to 360sccm, so that ammonia and hydrogen can achieve the same hydrogen concentration and flow rate when T=750°C and above for 100% decomposition of NH3 to H2 and N2. The cell performance is measured over a range of pressure (p=1, 3, 5atm) and temperatures (T=750, 800, 850°C). As to the study of fuel concentration, there are three different fuel concentrations for both hydrogen and ammonia fuels for comparison: (1) high concentration (675 sccm H2 + 225 sccm N2 and 450 sccm NH3); (2) medium concentration (450 sccm H2 + 450 sccm N2 and 300 sccm NH3 + 300 sccm N2); (3) low concentration (225 sccm H2 + 675 sccm N2 and 150 sccm NH3 + 600 sccm N2), all case using 900 sccm air in cathode. The result shows that the ammonia SOFC at current density of 350 Acm-2 and 850°C. When increasing p from 1 atm to 3 atm and 5 atm, the ammonia cell performance can be improved 9.6% and 14.9%, respectively. From EIS data, we find that the total polarization resistances decrease with increasing pressure. When the operating temperature increases from 750°C to 850°C, the cell performance at 0.8V can be increased by 28.9% (1 atm) and 27.1% (5 atm), respectively, showing that increasing the temperature can improve the cell performance due to the increases of the ionic conductivity of the electrolyte layer and the electron conductivity of the anode, resulting in the decrease of the ohmic impedance. The condition of changing the fuel concentration, as the fuel concentration increases, the polarization resistance decreases and the cell performance increases. The stability test of ammonia SOFC about 25 hours operation show that the power density can be maintained stable without any degradation at both 1 atm and 3 atm when the temperature is kept at 700°C at 0.8V. Hence, ammonia SOFC can be continuously operated at both atmospheric and elevated pressure conditions. These results are useful for the future development of pressurized ammonia SOFCs either in a portable device or an integration with micro gas turbines for power generation. | en_US |